#include "apue.h"
#include <fcntl.h>

int
main(int argc, char *argv[])
{
    int val;

    if(argc != 2)
        err_quit("usage: main.out <descriptor#>");

    // atoi means `ascii to integer`
    if( (val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
        err_sys("fcntl error for fd %d", atoi(argv[1]));

    // 按位与
    switch(val & O_ACCMODE){
        case O_RDONLY: 
            printf("read only");
            break;
        
        case O_WRONLY: 
            printf("write only");
            break;

        case O_RDWR: 
            printf("read write");
            break;

        default:
            err_dump("unknown access mode");
    }

    if(val & O_APPEND)
        printf(", append");
    if(val & O_NONBLOCK)
        printf(", nonblocking");
    if(val & O_SYNC)
        printf(", synchronous writes");

#if !defined(_POSIX_C_SOURCE) && defined(O_FSYNC) && (O_FSYNC != O_SYNC)
    if(val & O_FSYNC)
        printf(", synchronous writes");
#endif

    putchar('\n');
    exit(0);
}